The present invention generally relates to rectifier instruments for rectifying an output generated from an alternator for vehicles such as a car or the like and, more particularly, is directed to a vehicle alternator output rectifier instrument suitable for suppressing an over-voltage and for reducing a radio noise.
Recently, the kind of and the number of electronic devices that are mounted on vehicles as electrical loads have increased so remarkably that a malfunction of these electronic devices becomes a problem. To avoid the malfunction of the electronic devices, a DC (direct current) voltage that is obtained from a rectifier when the rectifier rectifies an output of an alternator driven by a car engine, must be prevented from generating an over-voltage.
In order to protect the electronic devices from the over-voltage, a conventional vehicle alternator output rectifier instrument employs as rectifier elements Zener diodes which cause a breakdown at a relatively low voltage as is disclosed in Japanese Published Patent Publication Nos. JP-2B-54-5083 and JP-A-63-240336.
When the Zener diodes are mounted on the car, the following points should be considered.
(1) Because the vehicle alternator output rectifier instrument is mounted in the engine room of the car, it is exposed to high temperature and utilized under severe temperature circumstances. PA1 (2) Because the vehicle alternator output rectifier instrument is constantly connected to a car battery even when the car is not driven, a reverse leakage current is generated through the rectifier elements within the rectifier instrument, resulting in the car battery being discharged. PA1 (3) A radio noise generated from the vehicle alternator output rectifier instrument has to be suppressed.